1. Field of the Invention
The present invention relates mainly to a reflection type display device, and to a direct viewing type display device which materializes high contrast and display in white by scattering reflected light. The present invention is particularly effective in a reflection type liquid crystal display device using a liquid crystal material having an electrooptical effect and in an applied product using such a display device (a portable information apparatus, a personal computer, a word processor, and the like).
It is to be noted that an electrooptical display device as used herein refers to any apparatus which functions by utilizing an electrooptical material. Therefore, the above-mentioned liquid crystal display device also falls within the category of electrooptical display devices. However, in this specification, for the sake of clarity, the term xe2x80x9ca liquid crystal display devicexe2x80x9d and the term xe2x80x9can electrooptical display devicexe2x80x9d are used differently.
2. Description of the Related Art
Recently, it has become common to display picture data and dynamic images at an information terminal such as a portable personal computer. In order to accommodate this trend, color picture display devices are materialized as transmission type display devices. Transmission type liquid crystal display devices are also widely used for displays in video cameras and digital cameras.
However, there is a problem that the power consumption of a back light limits the usable time of such a transmission type display device.
This leads to trial manufacture of many reflection type color display devices which can display pictures in 4,096 colors or more.
As conventional reflection type display devices, liquid crystal display devices for electronic calculators, various kinds of watches which are mainly wristwatches, electronic organizers, portable computers, and the like are known. Power consumption in those devices is lower than that of transmission type liquid crystal display devices because they do not use a back light. Therefore, they are highly demanded as direct viewing type display devices for portable computers, information terminals, and the like which are usable for a long time. As a result, reflection type color display devices are now required to be further improved with regard to the brightness and the contrast.
Further, conventional reflection type display devices display in black and white for technical and economical reasons. In this case, through the expression is xe2x80x9cblack and white,xe2x80x9d the white is not as white as paper, but is actually pale green or gray. This is due to the operation mode of the liquid crystal being used.
With regard to display of character information and symbols, this causes no particular problem in the practical aspect and this is also advantageous in the economical aspect.
With regard to the above-mentioned display devices of black and white type, brighter display which is almost as white as paper is desired.
FIG. 12 is a schematic view of an example of a conventional structure. In FIG. 12, switching elements 11 such as thin film transistors, an interlayer insulating film 12, pixel electrodes 13, an orientated layer 14-1, a liquid crystal layer 15, the orientated layer 14-2, and an opposing electrode 16 are formed between a substrate 10 and an opposing substrate 17 in this order from the top surface of the substrate 10. Also, incident light 20 is reflected by the pixel electrodes to cause reflected light 21. It is to be noted that, though FIG. 12 as a schematic view does not show the whole structure, many switching elements and many pixel electrodes are formed in matrix on the surface of the substrate 10.
The reflection type liquid crystal display device utilizes an optical modulation action of the liquid crystal as an electrooptical material, and materializes a state where incident light is reflected by a reflection electrode of a pixel to be emitted to the external of the device and a state where incident light is not emitted to carry out bright display and dark display, thereby displaying an image.
It is to be noted that silver may be used as the material of the reflection electrodes of the pixel portion. However, in spite of its high reflectance, since silver is difficult to be processed minutely and easy to be oxidize, so that the state of its surface is difficult to maintain, it is behind in applying to products except for some cases.
Therefore, it is common to use aluminum or aluminum alloy which are excellent in processability and have the reflectances of almost 92%. However, when they are practically used, being influenced by the refractive index of materials formed on the electrodes (the orientated layer and the like), the refractivity is lowered to about 85% even when only the interface loss of this portion is taken into consideration.
When liquid crystal is used, a region called disclination leading to a lowered refractivity is formed and there are loss and absorption at the interfaces existing in the path of light from entering to leaving. Thus, if all of these are taken into consideration, the refractivity is lowered to be as low as about 40-70%.
Further, when the reflected picture is directly viewed, since the electrodes macroscopically form a mirror surface, it is very difficult to view the display as it is. Thus, conventionally, the surface of the pixel electrodes formed of a metal material are lightly etched and a fine uneven portion is formed on the surface. Display in white is materialized by optically scattering incident light by the uneven portion. It is to be noted that the quantity of reflected light to be observed is remarkably lowered due to the scattering action.
A conventional reflection layer (pixel electrodes) does not provide sufficient reflection and irregular reflection of light (including diffusion and scattering of light), and thus, has the problem in brightness of insufficient brightness for a liquid crystal display device (in particular, a direct viewing reflection type liquid crystal panel).
Accordingly, an object of the invention disclosed herein is to solve the above-mentioned problem and to provide a direct viewing type display device and a manufacturing process of the same, the display device having higher contrast and brighter display with the white portion being closer to the color of white paper by improving the electrode refractivity of a reflection type display device compared with a conventional one.
According to one aspect of the present invention disclosed herein, there is provided an electrooptical display device comprising at least one substrate, an electrooptical material, a first electrode on the substrate, and a second electrode for applying an electric field on the electrooptical material, characterized by further comprising a texture body on the first electrode, and a light reflection film on the texture body formed of a material having a higher refractive index than that of the texture body.
The above structure is characterized in that the texture body has on its surface an uneven portion for diffusing light, the uneven portion being 1 xcexcm or less in height.
The above structure is characterized in that the light reflection film is flat and an uneven portion of the light reflection film is 0.3 xcexcm or less in height.
The above structure is characterized in that an interlayer insulating film exists below the texture body, the interlayer insulating film being flat with an uneven portion of the interlayer insulating film being 0.3 xcexcm or less in height.
The above structure is characterized in that the first electrode is formed of aluminum, a material with a main component thereof being aluminum, silver, or a material with a main component thereof being silver. The above structure is characterized in that the electrooptical material is formed of a nematic, a smectic, or a cholesteric liquid crystal material.
According to another aspect of the present invention disclosed herein, there is provided a reflection type electrooptical display device comprising a first substrate formed of a semiconductor substrate or an insulating substrate, a second substrate formed of a transparent substrate, and liquid crystal encapsulated between the substrates forming a pair, characterized in that a first electrode formed of a metal material, a texture body having a refractive index of 1.7 or less, and a light reflection film formed of a material having a higher refractive index than that of the texture body are provided on the first substrate, and in that a second electrode formed of a transparent material is provided on the second substrate.
In the above respective structures, when the film thickness and the refractive index of the texture body are given as d1 and n1, respectively, the film thickness d1 is adjusted to satisfy 300 nmxe2x89xa6xcexxe2x89xa6800 nm (wherein xcex=4n1d1) in a part of or substantially all over the texture body.
In the above respective structures, when the film thickness and the refractive index of the light reflection film are given as d2 and n2, respectively, the film thickness d2 is adjusted to satisfy 300 nmxe2x89xa6xcexxe2x89xa6800 nm (wherein xcex=4n2d2) in a part of or substantially all over the light reflection film.
The above respective structures are characterized in that the texture body is formed of SiO2, MgF2, Na3AlF6, an acrylic resin, or polyimide.
The above respective structures are characterized in that the light reflection film is formed of TiO2, ZrO2, Ta2O5, ZnS, ZnSe, ZnTe, Si, Ge, Y2O3, Al2O3, or Indium Tin Oxide.